The Nitrogen Cycle
By: Shreyan Patel, Hendrik Mayer,
Katie Roy, and Grant Liu
Overview
Nitrogen cannot be absorbed directly by the plants and animals until it is converted into
compounds they can use. This process is called the Nitrogen Cycle. Therefore, the two ways the
Nitrogen Cycle starts off is first in the soil where special bacteria form nitrates out of nitrogen in the
air. Another way is through lightning, because during electrical storms, large amounts of nitrogen are
oxidized and united with water to produce an acid that falls to Earth in rainfall and deposits nitrates in
the soil. Now since the nitrogen has been converted into nitrate, which can be absorbed by plants they
take up the nitrates and convert them to proteins that then travel up the food chain through
consumers. The cycle proceeds when theses consumers excrete waste, releasing nitrogen back into
the environment. When they die and decompose, the nitrogen is broken down and converted to
ammonia. Some of the ammonia is absorbed by plants, while the remainder stays in the soil, where it
converted back to nitrates. Two places the remaining nitrates may be stored in include, organic
materials or leached from the soil and carried into lakes and streams. They may also be converted to
gaseous nitrogen through a process called denitrification and returned to the atmosphere, continuing
the cycle.
Five steps of the Nitrogen Cycle
1. Nitrogen fixation
2. Nitrification
3. Assimilation
4. Ammonification
5. Denitrification
Step 1: Nitrogen Fixation
-
Nitrogen fixation is a process where the bacteria in the soil convert inert
nitrogen gas in the atmosphere into ammonia or nitrogen dioxide
The ammonia and nitrogen dioxide can then either be converted into other
compounds or absorbed by plants.
Step 2: Nitrification
is a process where
-
1. nitrosomonas, a type of bacteria, convert ammonium into nitrites
2. some of this is converted into nitrates by nitrosomonas, a type of bacteria
3. the nitrites and nitrates are then absorbed by plants
Step 3: Assimilation
This is the process where the nitrates and ammonia present in the soil
are absorbed through a plant’s roots.
Step 4: Ammonification
After all of the living organisms have used and absorbed the nitrogen, the
decomposers (bacteria) convert the waste (that is rich in nitrogen compounds)
into simpler ones. While the compounds are being converted into simpler ones,
ammonia is released.
Step 5: Denitrification
The final step in the nitrogen cycle, other bacteria convert the simple nitrogen
compounds back into nitrogen gas, this gas is then released back into the
atmosphere to begin the cycle again.
Ammonia, Nitrates, and Nitrites
Ammonia - A compound of nitrogen and hydrogen
- has the formula NH₃.
- is also known as azane
- it is a colorless gas with a pungent smell.
Nitrate - a nitrogen compound made from nitrites by a bacteria called nitrobacter; it is then
converted back into nitrates to be used by the plant; some nitrates are also transformed
back into gaseous nitrogen
Nitrite - a nitrogen compound made from ammonium by a species of bacteria called
nitrosomonas, it is then made into nitrates or absorbed directly into plant roots; nitrates are
transformed back into nitrites to be used in the plant
Eutrophication
A process which occurs when excess amounts of
compounds such as phosphorus and nitrogen are present in
the ecosystem. This process usually culminates in an
increase in cyanobacteria in the ecosystem
Impacts
Human activities, such as burning fossil fuels and using fertilizers, impact the
nitrogen cycle. These actions can lead to an increase in the amount of nitrogen
in the atmosphere, which causes multiple problems for terrestrial and aquatic
ecosystems. Terrestrial ecosystems may suffer from nutrient imbalance in trees,
changes in forest health, and declines in biodiversity. In aquatic ecosystems,
increases in nitrogen might cause fish to suffer from anoxia (no oxygen) and
hypoxia (low oxygen). There are also higher chances of harmful algae blooms
and acidification of freshwater sources. Since ecosystems around the globe
have many resources needed by humans, they are also affected.
Problem explanation
Animal and plant residues go into the soil (organic nitrogen) and are converted
to ammonium by bacteria in the soil. Other bacteria convert this ammonium into
nitrates. The nitrates converted coupled with the extra nitrates present in the
fertilizer create a surplus. This surplus is carried by water to the lake and
exacerbates the growth of algae in the water, which is the green surface present
on the lake. This covering of algae does not let oxygen or light penetrate the
water’s surface, causing the fish die from lack of oxygen.
Solutions
1.
2.
Ms. Schuckers and Mrs. Hinz could simply scoop the algae off of the top of
the lake and make daily disturbances in the surface. That way, light and
oxygen could penetrate the surface and allow fish to live.
Another solution could be to stop using the fertilizer. This would stop the
algae growth and allow the fish to repopulate. To stop the plants from
yellowing, they could use the dead fish to fertilize the plants similar to the
way that the Native Americans did.
Sources
http://www.nature.com/scitable/knowledge/library/the-nitrogen-cycleprocesses-players-and-human-15644632
http://extension.missouri.edu/p/WQ252
http://www.eoearth.org/view/article/154864/
http://www.nature.com/scitable/knowledge/library/the-nitrogen-cycleprocesses-players-and-human-15644632
https://www2.ucar.edu/news/backgrounders/nitrogen-earth-system